Fixed partial charge

When this equation is applied to a system composed of a macromolecule immersed in an aqueous medium containing a dissolved electrolyte, the fixed partial charges of each atom of the macromolecule result in a charge density described by p, and the mobile charges of the dissolved electrolyte are described by /O , which i derived from a Boltzmann distribution of the ions and coions. 

The fixed partial charge (FPC) model (35) assumes that the electrons follow the nuclear motion perfectly and serve merely to screen the nuclear charge. The dipole moment derivative contribution from each nucleus is (5R /9Ga)o where... 

Rotational and Dipole Strength Calculations for the CH-Stretching Vibrations of L-alanine Using the Localized Molecular Orbital, Nonlocalized Molecular Orbital, Atomic Polar Tensor, and Fixed Partial Charge Models ... 

The electrostatic embedding of MM partial charges as a perturbational potential in the Hamilton operator is a frequently used method to account for Coulombic interactions between QM atoms and MM point charges. As the respective potential contributions influence the quantum mechanical calculation and by that the molecular orbitals and the associated electron density, this approach is rated superior compared to a Coulombic interaction model utilising fixed partial charges. 

Optical excitations quite often generate considerable changes in fixed partial charges, usually described in terms of the difference solute dipole Amo ( 0 refers here to the solute). Chromophores with high magnitudes of the ratio Amo/Rl, where Rq is the effective solute radius, are often used as optical probes of the local solvent structure and solvation power. High polarizability changes are also quite common for optical chromophores, as is illustrated in Table 2. Naturally, the theory of ET reactions and optical transitions needs extension for the case when the dipole moment and polarizability both vary with electronic transition ... 

The fixed partial charge (FPC) model was first introduced by Deutsche and Moscowitz (1968) for polymers. Later on it was modified by Schellman (1973) to be used to predict the VCD of small molecules. 

Gel permeation chromatographic (GPC) analysis was not possible directly on the primary-amine-functionalized oligomers because of their tendency to be adsorbed on the GPC columns rather than to elute. A method has been developed in our laboratories (9, 10) for derivatization of the amine end groups with benzophenone to form an imine functionality. This method allows FPC (fixed-partial-charge) analysis of the oligomers. 

An expression which is structurally similar to the last term of equation 26 appears in the (conceptionally simple) fixed partial charge (FPC) model of vibrational CD In... 

Second, there are significant sources of errors in both the force field and continuum dielectric model used to approximate solvation effects. As an example, polarization effects are neglected in force fields based on fixed partial charges. A recent extension of the LIECE model has emphasized the importance of quantum mechanics to capture these effects, in particular for sets of inhibitors vith significant differences in the number of formal charges [114]. 

The additional computational effort, compared to fixed partial charges, is rather minor, i.e., about 15% for simulations of neat water [10,11] (the authors consider the TIP4P and SPC/E water models). Figure 3 shows an application of this technique to oligo(ethyleneoxide) in water [12]. This simulation contained a 7mer immersed in 1000 water molecules at ambient... 

Approximate models include the coupled oscillator (CO), the fixed partial charge (FPC),i7>i - o the charge flow (CF), the ring current, the... 

A. Annamalai, T. A. Keiderling, and J. S. Chickos, /. Am. Chem. Soc., 106, 6254 (1984). Vibrational Circular Dichroism of (rons-1,2-Dideuteriocyclobutane. A Comparison trf Fixed Partial Charge and Localized Molecular Orbital Theories with Different Force Fields. A. Annamalai, T. A. Keiderling, and J. S. Chickos, /. Am. Chem. Soc., 107, 2285 (1985). Vibrational Circular Dichroism of trans-1,2-Dideuteriocyclobutane. Experimental and Cal-culational Results in the Mid-Infrared. 

From the point of view of electrostatic interactions (that are obviously of crucial impxjrtance for the description of ionic liquids), there are two main choices fixed partial charges and polarizable models. 

More recently, force fields that account approximately for electronic polarization due to the strong electrostatic fields around nucleic acid molecules have become available (Babin et al. 2006). Additional terms often in the form of field-induced dipoles on atoms are used to approximately describe the deformation of the electron cloud due to an electrostatic field. It has been shown that such force field models can improve MD simulations of DNA resulting in overall better agreement with available experimental data than the standard force field form with fixed partial charges on atoms and no additional polarization term (Babin et al. 2006). 

Approximate models include the coupled oscillator (CO), the fixed partial charge (FPC), the chaige flow (CF), the ring current, the dynamic polarizability (DP), the bond dipole (BD), the localized molecular orbital (LMO) the nonlocalized molecular orbital (NMO), the atomic polar tensor (APT), and the locally distributed origins gauge... 

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